…tate

This change adds internal data structures that can be used for transactional
connection state. These data structures also reduces the amount of code that
is needed for each connection property that is added. Connection properties
are currently represented as actual variables in the ConnectionImpl class.
These new data structures removes the need for that.

Only the connection property retryAbortsInternally is refactored to use
the new data structure. All other connection properties will be refactored
in a following change, in order to keep each change as small as possible.

The data structure supports both transactional and non-transactional
connection state. Transactional state is disabled in the current version
in order to be consistent with the current behavior. It will be enabled
in a later change when all connection properties have been refactored
to use the new data structure.

Replace individual variables in ConnectionOptions and ConnectionImpl with
references to ConnectionProperties. This reduces the amount of code bloat,
especially in ConnectionOptions, as all connection property parsing is
now handled by the ConnectionState class in a generic way.

This setup also reduces the amount of code that is needed to add a new
connection property, as there is only one source of truth: the list of
properties in the ConnectionProperties class.

Following steps that will reduce the amount of code bloat further are:
1. Replace all the regular expressions for SET and SHOW statements with
   a simple token-based parser.
2. Cleaning up ConnectionOptions further by removing the duplicate list
   of ConnectionProperties there. These can be removed once the JDBC
   driver has been updated to use the new list of properties.

…tate

This change adds internal data structures that can be used for transactional
connection state. These data structures also reduces the amount of code that
is needed for each connection property that is added. Connection properties
are currently represented as actual variables in the ConnectionImpl class.
These new data structures removes the need for that.

Only the connection property retryAbortsInternally is refactored to use
the new data structure. All other connection properties will be refactored
in a following change, in order to keep each change as small as possible.

The data structure supports both transactional and non-transactional
connection state. Transactional state is disabled in the current version
in order to be consistent with the current behavior. It will be enabled
in a later change when all connection properties have been refactored
to use the new data structure.

Replace individual variables in ConnectionOptions and ConnectionImpl with
references to ConnectionProperties. This reduces the amount of code bloat,
especially in ConnectionOptions, as all connection property parsing is
now handled by the ConnectionState class in a generic way.

This setup also reduces the amount of code that is needed to add a new
connection property, as there is only one source of truth: the list of
properties in the ConnectionProperties class.

Following steps that will reduce the amount of code bloat further are:
1. Replace all the regular expressions for SET and SHOW statements with
   a simple token-based parser.
2. Cleaning up ConnectionOptions further by removing the duplicate list
   of ConnectionProperties there. These can be removed once the JDBC
   driver has been updated to use the new list of properties.

This change enables transactional connection state for the Connection API.
It can be enabled by default for PostgreSQL-dialect databases using a system
property, and is always an opt-in for GoogleSQL-dialect databases.

Transactional connection state can be enabled for any database connection
with the `connection_state_type` connection STARTUP property.

…al-connection-state